the built quality for iphone 5 is superb. it is not meant for you to use casing on it. it is for you to carry it nakedly to feel the aluminium texture and the slimness of the phone. putting casing on defy the purpose of Apple in reducing the size and weight. if you use it with care, there's no need of any casing for protection. i use mine naked, even if it get scratches, well, is there a phone out there that won't scratch after usage? don get over reacted.
just my 2 cents.